Advancements in the arts of plastic materials and fabrication methods make possible implementation of advanced designs of brachytherapy sources, particularly those sources that emit short-range radiation such as beta particles or low energy x-rays. These types of sources are used for treatment of various types of cancer such as tumors of the prostate, head and neck, lung, liver, breast and others. Typically they are implanted in the tumor, or in the tumor-invaded volume of tissue. There are two types of implants, permanent and temporary. As the categories imply, the temporary implants are associated with equipment for removal of the sources after a few hours or days of radiation treatment. Conversely, permanent implants are placed in the body and remain there for the life of the patient. This is possible because the permanently implanted sources contain a radioisotope with a relatively short half-life, so that the radiation is completely dissipated after a few months, during which time it has destroyed the cancer. And further, the materials of construction of the sources are biocompatible.
The radioisotopes most commonly used in permanent implants today are iodine-125 and palladium-103 encapsulated in very small metallic tubular containers, e.g. of typical approximate dimensions: 4.5 mm in length and 0.8 mm in diameter to form brachytherapy sources. However, the principles and methods taught herein apply as improvements to those and to other sources and source designs, such as custom-molded intracavity irradiators, using any of a variety of radioisotopes such as Pd103, I125, Ir192, Co60, Yb196, Sr89, Cs131 and P32. Only the short-lived radioisotopes are used in permanent implants.
Such sources used as permanent interstitial implants and with dimensions of approximately 4.5 mm in length and 0.8 mm in diameter are commonly referred to as seeds. Such seeds, are designed around material constraints which include requirements that a) the capsule must be sufficiently transparent to the curative radiation so that it does not unduly diminish or distort the radiation field around the seed, b) yet it must be visible to fluoroscopic or x-ray film examination, so that the physician can determine seed placement, c) it must be strong enough to prevent damage that might permit leakage of the radioactive source material out of the capsule, and d) all surfaces that are in contact with body tissue and fluids must be biocompatible. In addition, it is desirable for the seed to have a shape or other property that permits connecting seeds and spacers so that the implanted seeds are somewhat constrained from migration from the intended implant location.
Currently available seeds meet the above-identified constraints with varying success by balancing conflicting requirements such as strength vs. transparency of the capsule to the emitted curative radiation, or fluoroscopic visibility vs. uniform radiation field. In the following teaching it is shown how the use of a new class of materials to make seeds allows innovative new balances between the several conflicting requirements, with designs that have significant economic and medical advantages over currently available products.